PROJECT SUMMARY/ABSTRACT Music is a signature of the human experience. A ubiquitous, ancient, and uniquely human activity, music appears across societies with remarkable diversity and with particular significance early in the lifespan: infants have precocial music perception abilities and are highly motivated to listen to music, while parents often produce music for infants. Why are we musical? What features of music drive its effects on listeners? Can music be leveraged to improve infant and parent health? Human infants are helpless and need parents' attention to ensure their safety. A simple form of music, infant-directed song, may function as a potent form of parental attention. If so, then (1) infant-directed song should share features across all human cultures, (2) infant-directed song should reliably reduce infant distress, and (3) increases in the regularity of parents' use of infant-directed song should improve infant temperament and parent well-being. The specific aims of this research address each of these predictions: Aim 1: Determine the universal acoustical features of infant-directed song across human cultures. Corpus analyses of audio recordings from 100 societies will determine the infant-directed song's universal acoustical features, and experiments in children and adults will determine universals in performance style and content of infant-directed song. Aim 2: Test the short-term efficacy of infant-directed song for regulating distress in infants. With classic methods from infant temperament research, experiments will test infant-directed song's efficacy in reducing distress by randomly assigning parents to sing or speak to infants after distress is induced and testing the latency to recovery from distress. Further experiments isolate the acoustical features of music that produce the largest main effects. Aim 3: Examine long-term effects of parental song on infant temperament and parent well-being. Two longitudinal studies will determine the causal effects of increases in the use of infant-directed song on infant behavior and parent well-being. Infant data will be collected via a new smartphone app administering ecological momentary assessment and parent anxiety, happiness, and self-esteem will be tested via Implicit Association Tasks and self-reports. Impact. This research will create a variety of useful resources for the research community: a new, expanded corpus of music from many small-scale societies; validation of a new, minimally invasive physiological monitoring device for use in infants; a new method for measuring infant recovery from distress; a new video corpus of infant distress induction and recovery; and a new smartphone app for assessing infant temperament in the home. Further, this work will provide the first systematic characterization of the acoustical features that underlie infant-directed song, it will determine whether music is a particularly effective means of regulating infant behavior, and it will determine whether such effects generalize to long-term improvements in infant and parent health. These results will advance the basic science of music and may be directly applied to improving the quality of parent-infant interaction ? a key concern for the lives of families with young infants ? by leveraging infants' innate ability to perceive music and parents' innate ability to produce it.